Semiconductor device and method of fabricating the same

ABSTRACT

A display device includes a main body, a support stand, and a display portion. The display portion includes a pixel having a TFT and a capacitor. The capacitor includes a capacitor electrode on an insulating surface, an insulating film on the capacitor electrode, and a pixel electrode of the TFT on the insulating film.

BACKGROUND OF THE INVENTION Field of the Invention

The invention of the present application relates to a semiconductordevice having a circuit which is configured of thin film transistors(hereinbelow termed “TFTs”), and a method of fabricating thesemiconductor device. By way of example, it relates to an electroopticaldevice which is typified by a liquid crystal display panel, and anelectronic equipment in which such an electrooptical device is installedas a component.

Incidentally, here in this specification, the “semiconductor device” isintended to signify general devices which can function by utilizingsemiconductor properties, and electrooptical devices, semiconductorcircuits and electronic equipment are all the semiconductor devices.

Description of Related Art

In recent years, notice has been taken of technology wherein thin filmtransistors (TFTs) are constructed using a semiconductor thin film(having a thickness on the order of several—a few hundred nm) which isformed on a substrate having an insulating surface. The TFTs areextensively applied to ICs and electron devices such as electroopticaldevices, and it is especially hurried to develop them as the switchingelements of an image display device.

Hitherto, liquid crystal display devices have been known as imagedisplay devices. The liquid crystal display device of active matrix typehas come to be often employed because an image of higher definition thanby the liquid crystal display device of passive type can be obtained. Inthe active matrix type liquid crystal display device, a display patternis formed on a screen by driving pixel electrodes arranged in the shapeof a matrix. More specifically, voltages are applied between selectedones of the pixel electrodes and ones of counter electrodescorresponding to the selected pixel electrodes, whereby a liquid crystallayer interposed between the pixel electrodes and the counter electrodesis optically modulated, and the optical modulation is recognized as thedisplay pattern by an observer.

The applications of such an active matrix type liquid crystal displaydevice have widened, and a higher definition, a higher apertureefficiency and a higher reliability have been more required togetherwith the larger area of a screen size. Besides, enhancement inproductivity and reduction in cost have been more required at the sametime.

In the prior art, an amorphous silicon film is suitably employed as anamorphous semiconductor film for the reason that it can be formed on asubstrate of large area at a low temperature of or below 300. Also, TFTsof inverse stagger type (or bottom gate type) each having a channelforming region formed of an amorphous semiconductor film are oftenemployed.

BRIEF SUMMARY OF THE INVENTION

Heretofore, a liquid crystal display device of active matrix type hasbeen high in its manufacturing cost for the reason that TFTs have beenfabricated on a substrate by using, at least, five photo-masks inaccordance with photolithographic technology. In order to enhance aproductivity and to enhance an available percentage, decreasing thenumber of steps is considered as effective means.

Concretely, it is necessary to decrease the number of photo-masksrequired for the manufacture of TFTs. The photo-mask is employed forforming a photoresist pattern to serve as the mask of an etching step,over a substrate in the photolithographic technology.

Using each of the photo-masks, steps such as coating with a resist,pre-baking, exposure to light, image development and post-baking areperformed, and steps such as the formation and etching of a film andfurther steps such as stripping off the resist, washing and drying areadded as the preceding and succeeding steps of the first-mentionedsteps. These steps are complicated, and have been problematic.

Moreover, since the substrate is an insulator, static electricity hasbeen generated by friction etc. during the manufacturing process. Whenthe static electricity is generated, short-circuiting arises at theintersection part of wirings laid over the substrate, or the TFTs aredeteriorated or destroyed by the static electricity, so that displaydefects or degradation in an image quality have/has occurred in theliquid crystal display device. In particular, during the rubbing ofliquid crystal orientation processing which is performed in themanufacturing process, the static electricity appears and has beenproblematic.

The present invention consists in replying to such problems, and in asemiconductor device typified by a liquid crystal display device ofactive matrix type, it has for its object to decrease the number ofsteps for fabricating TFTs, thereby to realize reduction in amanufacturing cost and enhancement in an available percentage.

Also, it has for its object to provide a structure capable of solvingthe problem of the destruction of TFTs or the characteristicsdeterioration thereof ascribable to static electricity, and a method offabricating the structure.

In order to solve the problems, according to the present invention, eachgate wiring is initially formed by a first photo-mask.

Subsequently, a gate insulating film, a non-doped amorphous silicon film(hereinbelow, called “a-Si film”), an amorphous silicon film whichcontains an impurity element bestowing the n-type (hereinbelow, called“n⁺a-Si film”), and an electrically-conductive film are formed insuccession.

Subsequently, an active layer, a source wiring (including a electrode)and a drain electrode which are made of the a-Si film are patterned andformed by a second photo-mask.

Thereafter, a transparent electrically-conductive film is formed,whereupon a pixel electrode made of the transparent conductive film isformed by a third photo-mask. Further, a source region and a drainregion which are made of the n⁺a-Si film are formed, while at the sametime, part of the a-Si film is removed.

Owing to such a construction, the number of the photo-masks for use inphotolithographic technology can be made three.

Moreover, the source wiring is covered with the transparent conductivefilm which is the same material as that of the pixel electrode, therebyto form a structure in which the whole substrate is protected fromexternal static electricity etc. It is also allowed to form a structurein which a protective circuit is formed of the transparent conductivefilm. Owing to such a construction, the generation of the staticelectricity which is ascribable to the friction between a manufacturingapparatus and the insulator substrate can be prevented during amanufacturing process. In particular, TFTs etc. can be protected fromthe static electricity which appears during the rubbing of liquidcrystal orientation processing that is performed in the manufacturingprocess.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 View showing a top plan in the invention of the presentinvention.

FIG. 2 Sectional views showing the steps of fabricating an AM-LCD.

FIG. 3 Sectional views showing the steps of fabricating the AM-LCD.

FIG. 4 Top plan views showing the steps of fabricating the AM-LCD.

FIG. 5 Top plan views showing the steps of fabricating the AM-LCD.

FIG. 6 Top plan view for explaining the arrangement of the pixelportions and input terminal portions of the liquid crystal displaydevice.

FIG. 7 Sectional view showing the packaging structure of a liquidcrystal display device.

FIG. 8 Sectional view showing the step of fabricating an AM-LCD.

FIG. 9 Views showing examples of electronic equipment.

FIG. 10 Views showing examples of electronic equipment.

FIG. 11 Views showing examples of electronic equipment.

DETAILED DESCRIPTION OF THE INVENTION

The construction of an invention disclosed here in this specificationconsists in:

a semiconductor device having a gate wiring, a source wiring, and apixel electrode, characterized by comprising:

the gate wiring 102 which is formed on an insulating surface;

an insulating film 104 which is formed on said gate wiring;

an amorphous semiconductor film 114 which is formed on said insulatingfilm;

a source region 115 and a drain region 116 which are formed on saidamorphous semiconductor film;

the source wiring 117 or a electrode 118 which is formed on said sourceregion or said drain region; and

the pixel electrode 119 which is formed on said electrode;

wherein one end face of said drain region 116 or said source region 115lies substantially in register with an end face of said amorphoussemiconductor film 114 and an end face of said electrode 118.

Besides, the construction of another invention consists in:

a semiconductor device having a gate wiring, a source wiring, and apixel electrode, characterized by comprising:

the gate wiring 102 which is formed on an insulating surface;

an insulating film 104 which is formed on said gate wiring;

an amorphous semiconductor film 114 which is formed on said insulatingfilm;

a source region 115 and a drain region 116 which are formed on saidamorphous semiconductor film;

the source wiring 117 or a electrode 118 which is formed on said sourceregion or said drain region; and

the pixel electrode 119 which is formed on said electrode;

wherein one end face of said drain region 115 or said source 116 regionlies substantially in register with an end face 114 of said amorphoussemiconductor film and an end face of said electrode 118, and the otherend face thereof lies substantially in register with an end face of saidpixel electrode 119 and the other end face of said electrode 118.

DETAILED DESCRIPTION OF THE INVENTION

Also, the construction of another invention consists in:

a semiconductor device having a gate wiring, a source wiring, and apixel electrode, characterized by comprising:

the gate wiring 102 which is formed on an insulating surface;

an insulating film 104 which is formed on said gate wiring;

an amorphous semiconductor film 114 which is formed on said insulatingfilm;

a source region 115 and a drain region 116 which are formed on saidamorphous semiconductor film;

the source wiring 117 or a electrode 118 which is formed on said sourceregion or said drain region; and

the pixel electrode 119 which is formed on said electrode;

wherein said amorphous semiconductor film, and an amorphoussemiconductor film which contains an impurity element bestowing then-type are stacked below said source wiring 117.

Also, in each of the above constructions, the semiconductor device ischaracterized in that said source region and said drain region are madeof an amorphous semiconductor film which contains an impurity elementbestowing the n-type.

Also, in each of the above constructions, the semiconductor device ischaracterized in that said insulating film, said amorphous semiconductorfilm, said source region and said drain region are formed successivelywithout being exposed to the atmospheric air.

Also, in each of the above constructions, the semiconductor device ischaracterized in that said insulating film, said amorphous semiconductorfilm, said source region or said drain region is formed by a sputteringprocess.

Also, in each of the above constructions, the semiconductor device ischaracterized in that, as shown in FIG. 2(D), said source region 115 andsaid drain region 116 are formed by the same mask as that of saidamorphous semiconductor film 114 and said electrode 118. Alternatively,the semiconductor device is characterized in that said source region andsaid drain region are formed by the same mask as that of said sourcewiring 117.

Also, in each of the above constructions, the semiconductor device ischaracterized in that, as shown in FIG. 2(D), said source region 115 andsaid drain region 116 are formed by the same mask as that of said sourcewiring 117 and said pixel electrode 119.

Also, in each of the above constructions, owing to an etching step inFIG. 2(D), the semiconductor device has a construction where filmthicknesses in those regions of said amorphous semiconductor film whichare contiguous to said source region and said drain region are greaterthan a film thickness in that region of said amorphous semiconductorfilm which lies between the region contiguous to said source region andthe region contiguous to said drain region; that is, a bottom gatestructure of channel etching type.

Besides, the construction of an invention for realizing the abovestructure consists in:

a method of fabricating a semiconductor device characterized bycomprising:

the first step of forming each gate wiring 102 by employing a firstmask;

the second step of forming an insulating film 104 which covers the gatewiring;

the third step of forming a first amorphous semiconductor film 105 onsaid insulating film;

the fourth step of forming a second amorphous semiconductor film 106which contains an impurity element bestowing the n-type, on said firstamorphous semiconductor film;

the fifth step of forming a first electrically-conductive film 107 onsaid second amorphous semiconductor film;

the sixth step of forming a wiring 111 (source wiring and electrode) insuch a way that said first amorphous semiconductor film, said secondamorphous semiconductor film and the first conductive film areselectively removed by employing a second mask;

the seventh step of forming a second electrically-conductive film 112which overlies said wiring 111 (source wiring and electrode) and saidelectrode in touch with them; and

the eighth step of forming a source region 115 and a drain region 116made of said second amorphous semiconductor film, and a pixel electrode119 made of the second conductive film, in such a way that part of saidfirst amorphous semiconductor film 109, said second amorphoussemiconductor film 110, said first conductive film 111 and said secondconductive film 112 are selectively removed by employing a third mask.

Also, in the above construction, the method is characterized in thatsaid second step through said fifth step are performed successivelywithout exposure to the atmospheric air.

Also, in each of the above constructions, the method is characterized inthat said second step through said fifth step are performed successivelywithin an identical chamber.

Also, in each of the above constructions, said insulating film may wellbe formed by a sputtering process or a plasma CVD process.

Also, in each of the above constructions, said first amorphoussemiconductor film may well be formed by a sputtering process or aplasma CVD process.

Also, in each of the above constructions, said second amorphoussemiconductor film may well be formed by a sputtering process or aplasma CVD process.

Also, in each of the above constructions, the method is characterized inthat said second conductive film is a transparentelectrically-conductive film or an electrically-conductive film having areflectivity.

Modes for Carrying Out the Invention

Modes for carrying out the invention of the present application will bedescribed below.

FIG. 1 exemplifies a plan view of an active matrix substrate in thepresent invention, and the construction of one of a plurality of pixelsarranged in the shape of a matrix is illustrated here for the sake ofbrevity.

As shown in FIG. 1, the active matrix substrate has a plurality of gatewirings which are laid in parallel with one another, and a plurality ofsource wirings which intersect orthogonally to the individual gatewirings.

Besides, a pixel electrode 119 made of a transparentelectrically-conductive film is located in a region which is surroundedwith the gate wirings and the source wirings. In addition, a transparentelectrically-conductive film 120 covers the source wiring so as not tooverlap the pixel electrode 119.

Further, a capacitor wiring 103 is laid between the two gate wiringsadjoining below the pixel electrode 119, and in parallel with the gatewirings 102. The capacitor wiring 103 is disposed for each of all thepixels, and it forms a retention capacitor with a dielectric being aninsulating film which exists between it and the pixel electrode 119.

Besides, a TFT as a switching element is disposed in the vicinity of theintersection part between the gate wiring 102 and the source wiring 117.The TFT is one of inverse stagger type (or bottom gate type) whichincludes a channel forming region formed of a semiconductor film havingan amorphous structure (hereinbelow, called “amorphous semiconductorfilm”).

In addition, the TFT is such that a gate electrode (formed integrallywith the gate wiring 102), a gate insulating film, an a-Si film, asource region as well as a drain region made of an n⁺a-Si film, and aelectrode (formed integrally with the source wiring 117) as well as anelectrode 118 (hereinbelow, also called “drain electrode”) aresuccessively stacked and formed on the insulating substrate.

Also, a gate insulating film, an a-Si film and an n⁺a-Si film aresuccessively stacked and formed on the insulating substrate, under thesource wiring (including the electrode) as well as the drain electrode118.

Also, that region of the a-Si film which lies between the region thereofcontiguous to the source region and the region thereof contiguous to thedrain region has a smaller film thickness as compared with the otherregion thereof. The smaller film thickness is grounded on the fact that,in forming the source region and the drain region by separating then⁺a-Si film by etching, the part of the a-Si film has been removed.Moreover, the end face of the pixel electrode, that of the drain wiringand that of the drain region lie in register owing to the etching.Likewise, the end face of the transparent conductive film covering theelectrode, that of the source region and that of the source wiring liein register.

The invention of the present application constructed as stated abovewill be described in more detail in connection with embodiments givenbelow.

Embodiments of the Invention Embodiment 1

An embodiment of the invention is explained using FIGS. 1 to 6.Embodiment 1 shows a method of manufacturing a liquid crystal displaydevice, and a detailed explanation of a method of forming a TFT of apixel portion on a substrate by a reverse stagger type TFT, andmanufacturing a storage capacitor connected to the TFT, is made inaccordance with the processes used. Further, a manufacturing process fora terminal section, formed in an edge portion of the substrate, and forelectrically connecting to wirings of circuits formed on the othersubstrate, is shown at the same time in the same figures.

In FIG. 2(A), a glass substrate, comprising such as barium borosilicateglass or aluminum borosilicate glass, typically Corning Corp. #7059 or#1737, can be used as a substrate 100 having translucency. In addition,a translucent substrate such as a quartz substrate or a plasticsubstrate can also be used.

Next, after forming a conductive layer over the entire surface of thesubstrate, a first photolithography process is performed, a resist maskis formed, unnecessary portions are removed by etching, and wirings andelectrodes (the gate wiring 102 including a gate electrode, a capacitorwiring 103 and a terminal 101) are formed. Etching is performed at thistime to form a tapered portion in at least an edge portion of the gateelectrode 102. A top view of this stage is shown in FIG. 4.

It is preferable to form the gate wiring 102 including the gateelectrode, the capacitor wiring 103, and the edge portion terminal 101from a low resistivity conductive material such as aluminum (Al), butsimple Al has problems such as inferior heat resistance and easilycorrodes, etc., and therefore it is formed in combination with a heatresistant conductive material. One element selected from the groupconsisting of titanium (Ti), tantalum (Ta), tungsten (W), molybdenum(Mo), chromium (Cr), neodymium (Nd), or an alloy comprising the aboveelements, or an alloy film of a combination of the above elements, or anitrated compound comprising the above elements is formed as the heatresistant conductive material. Furthermore, forming in combination witha heat resistant conductive material such as Ti, Si, Cr, or Nd, it ispreferable because of improved levelness. Further, only such heatresistant conductive material may also be formed, for example,combination of Mo and W may be formed.

In realizing the liquid crystal display device, it is preferable to formthe gate electrode and the gate wiring by a combination of a heatresistant conductive material and a low resistivity conductive material.An appropriate combination in this case is explained.

Provided that the screen size is on the order of, or less than, 5 inchdiagonal type, a two layer structure of a lamination of a conductivelayer (A) made from a nitride compound of a heat resistant conductivematerial, and a conductive layer (B) made from a heat resistantconductive material is used. The conductive layer (B) may be formed froman element selected from the group consisting of Al, Ta, Ti, W, Nd, andCr, or from an alloy of the above elements, or from an alloy film of acombination of the above elements, and the conductive layer (A) isformed from a film such as a tantalum nitride (TaN) film, a tungstennitride (WN) film, or a titanium nitride (TiN) film. For example, it ispreferable to use a double layer structure of a lamination of Cr as theconductive layer (A) and Al containing Nd as the conductive layer (B).The conductive layer (A) is given a thickness of 10 to 100 nm(preferably between 20 and 50 nm), and the conductive layer (B) is madewith a thickness of 200 to 400 nm (preferably between 250 and 350 nm).

On the other hand, in order to be applied to a large screen, it ispreferable to use a three layer structure of a lamination of aconductive layer (A) made from a heat resistant conductive material, aconductive layer (B) made from a low resistivity conductive material,and a conductive layer (C) made from a heat resistant conductivematerial. The conductive layer (B) made from the low resistivityconductive material is formed from a material comprising aluminum (Al),and in addition to pure Al, Al containing between 0.01 and 5 atomic % ofan element such as scandium (Sc), Ti, Nd, or silicon (Si) is used. Theconductive layer (C) is effective in preventing generation of hillocksin the Al of the conductive layer (B). The conductive layer (A) is givena thickness of 10 to 100 nm (preferably between 20 and 50 nm), theconductive layer (B) is made from 200 to 400 nm thick (preferablebetween 250 and 350 nm), and the conductive layer (C) is from 10 to 100nm thick (preferably between 20 and 50 nm). In Embodiment 1, theconductive layer (A) is formed from a Ti film with a thickness of 50 nm,made by sputtering with a Ti target, the conductive layer (B) is formedfrom an Al film with a thickness of 200 nm, made by sputtering with anAl target, and the conductive layer (C) is formed from a 50 nm thick Tifilm, made by sputtering with a Ti target.

An insulating film 104 is formed next on the entire surface. Theinsulating film 104 is formed using sputtering, and has a film thicknessof 50 to 200 nm.

For example, a silicon oxynitride film is used as the insulating film104, and formed to a thickness of 150 nm. Of course, the gate insulatingfilm is not limited to this type of silicon oxynitride film, and anotherinsulating film such as a silicon oxide film, a silicon nitride film, ora tantalum oxide film may also be used, and the gate insulating film maybe formed from a single layer or a lamination structure made from thesematerials. For example, a lamination structure having a silicon nitridefilm as a lower layer and a silicon oxide film as an upper layer may beused.

Next, an amorphous semiconductor film 105 is formed with a thickness of50 to 200 nm (preferably between 100 and 150 nm) on the insulating film104 over the entire surface by using a known method such as plasma CVDor sputtering (not shown in the figure). Typically, a hydrogenatedamorphous silicon (a-Si:H) film is formed with a thickness of 100 nm bysputtering. In addition, it is also possible to apply a microcrystallinesemiconductor film, or a compound semiconductor film having an amorphousstructure, such as an amorphous silicon germanium film, etc., as theamorphous semiconductor film.

An amorphous semiconductor film 106 which contains an impurity elementimparting n-type is formed next with a thickness of 20 to 80 nm, as asemiconductor film containing impurity element of one conductivity type106. The amorphous semiconductor film which contains an impurity elementimparting n-type 106 is formed on the entire surface by a known methodsuch as plasma CVD or sputtering. Typically an n⁺a-Si:H film may beformed, and the film is deposited by using a target added withphosphorus (P) for that purpose. Alternatively, the amorphoussemiconductor film containing an n-type impurity element 106 may also beformed from a hydrogenated microcrystalline silicon film (μc-Si:H).

Next, a conductive metal film 107 is formed by sputtering or vacuumevaporation. Provided that ohmic contact with the n⁺a-Si:H film 106 canbe made, there are no particular limitation on the material of theconductive metal film 107, and an element selected from the groupconsisting of Al, Cr, Ta, and Ti, or an alloy comprising the aboveelements, and an alloy film of a combination of the above elements orthe like can be given. Sputtering is used in Embodiment 1, and a 50 to150 nm thick Ti film, an aluminum (Al) film with a thickness between 300and 400 nm above the Ti film, and a Ti film with a thickness of 100 to150 nm thereon are formed as the metal film 107. (See FIG. 2A.)

The insulating film 104, the amorphous semiconductor film 105, theamorphous semiconductor film 106 containing an impurity element whichimparts one conductivity type, and the conductive metal film 107 are allmanufactured by a known method, and can be manufactured by plasma CVD orsputtering. These films are formed in succession by sputtering, andsuitably changing the target or the sputtering gas in Embodiment 1. Thesame reaction chamber, or a plurality of reaction chambers, in thesputtering apparatus is used at this time, and it is preferable tolaminate these films in succession without exposure to the atmosphere.By thus not exposing the films to the atmosphere, the mixing in ofimpurities can be prevented.

Next, a second photolithography process is then performed, a resist mask108 is formed, and by removing unnecessary portions by etching, wiringand electrodes (source wiring) are formed. Wet etching or dry etching isused as the etching process at this time. The amorphous semiconductorfilm 105, the semiconductor film 106 containing an impurity elementwhich imparts one conductivity type and the conductive metal film 107are etched, and an amorphous semiconductor film 109, a semiconductorfilm 110 containing an impurity element which imparts one conductivitytype and a conductive metal film 111 are formed in the pixel TFTportion. Further, the capacitor wiring 103 and the insulating film 104remain in a capacitor portion, and the terminal 101 and the insulatingfilm 104 also remain similarly in a terminal portion. In Embodiment 1,the metal film 107 in which the Ti film, the Al film, and the Ti filmare laminated in order is etched by dry etching using a gas mixture ofSiCl₄, CL₂, and BCl₃ as a reaction gas, and the reaction gas issubstituted with a gas mixture of CF₄ and O₂, and the amorphoussemiconductor film 105 and the semiconductor film 106 containing theimpurity element for imparting one conductivity type, are removed. (SeeFIG. 2B.)

Next, after removing the resist mask 108, a transparent conductive film112 is deposited on the entire surface. (FIG. 2C) The top view at thistime is shown in FIG. 5. Note that the transparent conductive film 112deposited on the entire surface is not shown in FIG. 5 forsimplification.

This transparent conductive film 112 is formed from a material such asindium oxide (In₂O₃) or indium oxide tin oxide alloy (In₂O₃-SnO₂,abbreviated as ITO) using a method such as sputtering or vacuumevaporation. The etching process for this type of material is performedusing a solution of hydrochloric acid type. However, a residue is easilygenerated, particularly by ITO etching, and therefore an indium oxidezinc oxide alloy (In₂O₃-ZnO) may be used in order to improve the etchingworkability. The indium oxide zinc oxide alloy has superior surfacesmoothing characteristics, and has superior thermal stability comparedto ITO, and therefore even if the electrode 111 is made from an Al film,a corrosion reaction can be prevented. Similarly, zinc oxide (ZnO) isalso a suitable material, and in addition, in order to increase thetransmissivity of visible light and increase the conductivity, amaterial such as zinc oxide in which gallium (Ga) is added (ZnO:Ga) canbe used.

Resist mask 113 is formed next by a third photolithography process.Unnecessary portions are then removed by etching, forming an amorphoussemiconductor film 114, a source region 115, a drain region 116, thesource electrode 117, the drain electrode 118, and the pixel electrode119. (See FIG. 2D.)

The third photolithography process patterns the transparent conductivefilm, and at the same time removes a part of the conductive metal film111, the n⁺a-Si film 110 and the amorphous semiconductor film 109 byetching, forming an opening. In Embodiment 1, the pixel electrode madefrom ITO is selectively removed first by wet etching using a mixedsolution of nitric acid and hydrochloric acid, or a ferric chloridesolution, and a portion of the conductive metal film 111, the n⁺a-Sifilm 110 and the amorphous semiconductor film 109 are etched by dryetching. Note that wet etching and dry etching are used in Embodiment 1,but the operator may perform only dry etching by suitably selecting thereaction gas, and the operator may perform only wet etching by suitablyselecting the reaction solution.

The lower portion of the opening reaches the amorphous semiconductorfilm, and the amorphous semiconductor film 114 having a concave portionis formed. The conductive metal film 111 is separated into the sourcewiring 117 and the drain electrode 118 by the opening, and the n⁺a-Sifilm 110 is separated into the source region 115 and the drain region116. Furthermore, the transparent conductive film 120 contacting thesource electrode 117 covers the source wiring, and during subsequentmanufacturing processes, especially during a rubbing process, fulfills arole of preventing static electricity from developing. An example offorming the transparent conductive film 120 on the source wiring isshown in Embodiment 1, but the transparent conductive film 120 may alsobe removed during etching of the above stated ITO film. Further, acircuit for protection from static electricity may be formed byutilizing the above ITO film, in the etching of the ITO film.

Moreover, a storage capacitor is formed in the third photolithographyprocess by the capacitor wiring 103 and the pixel electrode 119, withthe insulating film 104 in the capacitor portion as a dielectric.

In addition, the transparent conductive film formed in the terminalportion is removed by the third photolithography process.

Next after removing the resist mask 113, a resist mask is formed byusing a shadow mask, and the insulating film which covers the terminal101 of the terminal portion is selectively removed. (FIG. 3A) Inaddition, the resist mask may also be formed by screen printing in placeof the shadow mask. Note that FIG. 1 is a top view of one pixel, andFIG. 3A corresponds to cross sections taken along the lines A-A′ and

B-B′.

By thus using three photomasks and performing three photolithographyprocesses, the pixel TFT portion having the reverse stagger typen-channel TFT 201 and the storage capacitor 202 can be completed. Byplacing these in a matrix state corresponding to each pixel and thuscomposing the pixel portion, one substrate can be made in order tomanufacture an active matrix liquid crystal display device. Forconvenience, this type of substrate is referred to as an active matrixsubstrate throughout this specification.

An alignment film 121 is selectively formed next in only the pixelportion of the active matrix substrate. Screen printing may be used as amethod of selectively forming the alignment film 121, and a method ofremoval in which a resist mask is formed using a shadow mask afterapplication of the alignment film may also be used. Normally, apolyimide resin is often used in the alignment film of the liquidcrystal display element. Note that though the present Embodiment showedan example of forming the alignment film after selectively removing theinsulating film which covers the terminal 101 of the terminal portion,the insulating film and the alignment film in the terminal portion maybe removed at the same time after laminating the alignment film on theinsulating film which covers the terminal 101 of the terminal portion.

Next, a rubbing process is then performed on the alignment film 121,orienting the liquid crystal elements so as to possess a certain fixedpre-tilt angle.

The active matrix substrate, and an opposing substrate 124 on which anopposing electrode 122 and an alignment film 123 are formed, are nextjoined together by a sealant while maintaining a gap between thesubstrates using spacers, after which a liquid crystal material 125 isinjected into the space between the active matrix substrate and theopposing substrate. A known material may be applied for the liquidcrystal material 125, and a TN liquid crystal is typically used. Afterinjecting the liquid crystal material, the injecting entrance is sealedby a resin material.

Next, a flexible printed circuit (FPC) is connected to the terminal 101of the terminal portion. The FPC is formed by a copper wiring 128 on anorganic resin film 129 such as polyimide, and is connected to the inputterminal 502 by an anisotropic conductive adhesive. The anisotropicconductive adhesive comprises an adhesive 126 and particles 127, with adiameter of several tens to several hundred of μm and having aconductive surface plated by a material such as gold, which are mixedtherein. The particles 127 form an electrical connection in this portionby connecting the input terminal 101 and the copper wiring 128. Inaddition, in order to increase the mechanical strength of this region, aresin layer 130 is formed. (See FIG. 3B.)

FIG. 6 is a diagram explaining the placement of the pixel portion andthe terminal portion of the active matrix substrate. A pixel portion 211is formed on a substrate 210, gate wirings 208 and source wirings 207are formed intersecting on the pixel portion, and the n-channel TFT 201connected to this is formed corresponding to each pixel. The pixelelectrode 119 and a storage capacitor 202 are connected to the drainside of the n-channel TFT 201, and the other terminal of the storagecapacitor 202 is connected to a capacitor wiring 209. The structure ofthe n-channel TFT 201 and the storage capacitor 202 is the same as thatof the n-channel TFT 201 and the storage capacitor 202 shown by FIG. 3A.

An input terminal portion 205 for inputting a scanning signal is formedin one edge portion of the substrate, and is connected to a gate wiring208 by a connection wiring 206. Further, an input terminal portion 203for inputting an image signal is formed in the other edge portion, andis connected to a source wiring 207 by a connection wiring 204. Aplurality of the gate wiring 208, the source wiring 207, and thecapacitor wiring 209 are formed in accordance with the pixel density,and their number are as described above. Furthermore, an input terminalportion 212 for inputting an image signal and a connection wiring 213may be formed, and may be connected to the source wiring alternatelywith the input terminal portion 203. An arbitrary number of the inputterminal portions 203, 205, and 212 are formed, which may be suitablydetermined by the operator.

Embodiment 2

FIG. 7 is an example of a method of mounting a liquid crystal displaydevice. The liquid crystal display device has an input terminal portion302 formed in an edge portion of a substrate 301 on which TFTs areformed, and as shown by embodiment 1, this is formed by a terminal 303formed from the same material as a gate wiring. An opposing substrate304 is joined to the substrate 301 by a sealant 305 encapsulatingspacers 306, and in addition, polarizing plates 307 and 308 are formed.This is then fixed to a casing 321 by spacers 322.

Note that the TFT obtained in Embodiment 1 having an active layer formedby an amorphous semiconductor film has a low electric field effectmobility, and only approximately 1 cm²/Vsec is obtained. Therefore, adriver circuit for performing image display is formed by a LSI chip, andmounted by a TAB (tape automated bonding) method or by a COG (chip onglass) method. In Embodiment 2, an example is shown of forming thedriver circuit in a LSI chip 313, and mounting by using the TAB method.A flexible printed circuit (FPC) is used, and the FPC is formed by acopper wiring 310 on an organic resin film 309, such as polyimide, andis connected to the input terminal 302 by an anisotropic conductiveadhesive. The anisotropic conductive adhesive is structured by anadhesive 311 and particles 312, with a diameter of several tens toseveral hundred of μm and having a conductive surface plated by amaterial such as gold, which are mixed therein. The particles 312 forman electrical connection in this portion by connecting the inputterminal 302 and the copper wiring 310. In addition, in order toincrease the mechanical strength of this region, a resin layer 318 isformed.

The LSI chip 313 is connected to the copper wiring 310 by a bump 314,and is sealed by a resin material 315. The copper wiring 310 is thenconnected to a printed substrate 317 on which other circuits such as asignal processing circuit, an amplifying circuit, and a power supplycircuit are formed, through a connecting terminal 316. A light source319 and a light conductor 320 are formed on the opposing substrate 304and used as a back light in the transmission type liquid crystal displaydevice.

Embodiment 3

In Embodiment 1 an example centering on forming lamination of aninsulating film, an amorphous semiconductor film, an amorphoussemiconductor film containing an impurity element which imparts n-typeconductivity, and a metal film by sputtering, but Embodiment 3 shows anexample of using plasma CVD to form the films.

The insulating film, the amorphous semiconductor film, and the amorphoussemiconductor film containing an impurity element which imparts n-typeconductivity are formed by plasma CVD in Embodiment 3.

In Embodiment 3, a silicon oxynitride film is used as the insulatingfilm, and formed with a thickness of 150 nm by plasma CVD. Plasma CVDmay be performed at this point with a power supply frequency of 13 to 70MHz, preferably between 27 and 60 MHz. By using a power supply frequencyof 27 to 60 MHz, a dense insulating film can be formed, and the voltageresistance can be increased as a gate insulating film. Further, asilicon oxynitride film manufactured by adding O₂ to SiH₄ and N₂O has areduction in fixed electric charge density in the film, and therefore isa material which is preferable for this use. Of course, the gateinsulating film is not limited to this type of silicon oxynitride film,and a single layer or a lamination structure using other insulatingfilms such as s silicon oxide film, a silicon nitride film, or atantalum nitride film may be formed. Further, a lamination structure ofa silicon nitride film in a lower layer, and a silicon oxide film in anupper layer may be used.

For example, when using a silicon oxide film, it can be formed by plasmaCVD using a mixture of tetraethyl orthosilicate (TEOS) and O₂, with thereaction pressure set to 40 Pa, a substrate temperature of 250 to 350°C., and discharge at a high frequency (13.56 MHz) power density of 0.5to 0.8 W/cm². Good characteristics as the gate insulating film can beobtained for the silicon oxide film thus formed by a subsequent thermalanneal at 300 to 400° C.

Typically, a hydrogenated amorphous silicon (a-Si:H) film is formed witha thickness of 100 nm by plasma CVD as the amorphous semiconductor film.At this point, plasma CVD may be performed with a power supply frequencyof 13 to 70 MHz, preferably between 27 and 60 MHz, in the plasma CVDapparatus. By using a power frequency of 27 to 60 MHz, it becomespossible to increase the film deposition speed, and the deposited filmis preferable because it becomes an a-Si film having a low defectdensity. In addition, it is also possible to apply a microcrystallinesemiconductor film and a compound semiconductor film having an amorphousstructure, such as an amorphous silicon germanium film, as the amorphoussemiconductor film.

Further, if 100 to 100 kHz pulse modulation discharge is performed inthe plasma CVD film deposition of the insulating film and the amorphoussemiconductor film, then particle generation due to the plasma CVD gasphase reaction can be prevented, and pinhole generation in the formedfilm can also be prevented, and therefore is preferable.

Further, in Embodiment 3 an amorphous semiconductor film containing animpurity element which imparts n-type conductivity is formed with athickness of 20 to 80 nm as a semiconductor film containing a singleconductivity type impurity element. For example, an a-Si:H filmcontaining an n-type impurity element may be formed, and in order to doso, phosphine (PH₃) is added at a 0.1 to 5% concentration to silane(SiH₄). Alternatively, a hydrogenated microcrystalline silicon film(μc-Si:H) may also be used as a substitute for the amorphoussemiconductor film 106, containing an impurity element which impartsn-type conductivity.

These films can be formed in succession by appropriately changing thereaction gas. Further, these films can be laminated successively withoutexposure to the atmosphere at this time by using the same reactionchamber or a plurality of reaction chambers in the plasma CVD apparatus.By thus depositing successively these films without exposing the filmsto the atmosphere, the mixing in of impurities into the first amorphoussemiconductor film can be prevented.

Note that it is possible to combine Embodiment 4 with Embodiment 2.

Embodiment 4

In Embodiment 4, an example of forming a protecting film is shown inFIG. 6. Note that Embodiment 4 is identical to Embodiment 1 through thestate of FIG. 2D, and therefore only points of difference are explained.Further, the same symbols are used for locations corresponding to thosein FIG. 2D.

After first obtaining the state of FIG. 2D in accordance with Embodiment1, a thin inorganic insulating film is formed on the entire surface. Asthe thin inorganic insulating film, a single layer or a laminatestructure may be formed by using inorganic insulating films such as asilicon oxide film, a silicon nitride film, a silicon oxynitride film ora tantalum oxide film.

A forth photolithography process is performed next, forming a resistmask, and unnecessary portions are removed by etching, forming aninsulating film 401 in the pixel TFT portion, and an inorganicinsulating film 402 in the terminal portion. These inorganic insulatingfilms 401 and 402 function as passivation films. Further, in theterminal portion, the thin inorganic insulating film 402 and theinorganic insulating film 104 are removed at the same time by the fourthlithography process, and the terminal 101 of the terminal portion can beexposed.

The reverse stagger type n-channel type TFT and the storage capacitor,protected by the inorganic insulating film, can thus be completed inEmbodiment 4 by performing the photolithography process using fourphotomasks four times in total. By thus structuring the pixel portion byarranging these into a matrix state corresponding to each pixel, onesubstrate for manufacturing the active matrix electro-optical device canbe made.

Note that it is possible to freely combine the constitution ofEmbodiment 4 with any one of constitutions of Embodiments 1 to 3.

Embodiment 5

Whereas the method of fabricating the active matrix substrate whichcorresponds to the liquid crystal display device of transmission typehas been mentioned in Embodiment 1, an example which corresponds to aliquid crystal display device of reflection type will be mentioned inthis embodiment.

First, up to the steps shown in FIG. 2(B) are carried out in the sameway as in Embodiment 1. Besides, an electrically-conductive film havinga reflectivity (of Al, Ag or the like) is formed instead of thetransparent electrically-conductive film. Besides, a resist mask patternis formed by the third photolithographic step in the same way as inEmbodiment 1, and a pixel electrode made of the reflective conductivefilm is formed by etching. The pixel electrode is formed so as tooverlap the electrode 118.

The subsequent steps are similar to those of Embodiment 1, and shalltherefore be omitted from description. In this way, the active matrixsubstrate corresponding to the reflection type liquid crystal displaydevice can be fabricated using three photo-masks by the threephotolithographic steps.

It is also possible to combine this embodiment with Embodiment 4.

Embodiment 6

CMOS circuits and pixel portion formed by implementing the presentinvention can be used in various electro-optical devices (such as anactive matrix liquid crystal display device and an active matrix ECdisplay device). Namely, the present invention can be implemented in allelectronic appliances in which these electro-optical devices are builtinto a display portion.

The following can be given as such electronic appliance: a video camera,a digital camera, a projector (rear type or front type), a head-mounteddisplay (goggle type display), a car navigation system, a car stereo, apersonal computer, and a portable information terminal (such as a mobilecomputer, a portable telephone or an electronic book). Examples of theseare shown in FIGS. 9, 10 and 11.

FIG. 9A is a personal computer, and it includes a main body 2001, animage input portion 2002, a display portion 2003, and a keyboard 2004,etc. The present invention can be applied to the image input portion2002, the display portion 2003 or other signal driver circuits.

FIG. 9B is a video camera, and it includes a main body 2101, a displayportion 2102, an audio input portion 2103, operation switches 2104, abattery 2105, and an image receiving portion 2106, etc. The presentinvention can be applied to the display portion 2102 or other signaldriver circuits.

FIG. 9C is a mobile computer, and it includes a main body 2201, a cameraportion 2202, an image receiving portion 2203, operation switches 2204,and a display portion 2205. The present invention can be applied to thedisplay portion 2205 or other signal driver circuits.

FIG. 9D is a goggle type display, and it includes a main body 2301, adisplay portion 2302, an arm portion 2303, etc. The present inventioncan be applied to the display portion 2302 or other signal drivercircuits.

FIG. 9E is a player that uses a recording medium on which a program isrecorded (hereafter referred to as a recording medium), and the playerincludes a main body 2401, a display portion 2402, a speaker portion2403, a recording medium 2404, and operation switches 2405, etc. Notethat this player uses a recording medium such as a DVD (digitalversatile disk) or a CD, and the appreciation of music, the appreciationof film, game playing and the Internet can be performed. The presentinvention can be applied to the display portion 2402 or other signaldriver circuits.

FIG. 9F is a digital camera, and it includes a main body 2501, a displayportion 2502, an eyepiece portion 2503, operation switches 2504, and animage receiving portion (not shown in the figure), etc. The presentinvention can be applied to the display portion 2502 or other signaldriver circuits.

FIG. 10A is a front projector, and it includes a projection system 2601,a screen 2602, etc. The present invention can be applied to a liquidcrystal display device 2808 which constitutes a part of the projectionsystem 2601, or other signal driver circuits.

FIG. 10B is a rear projector, and it includes a main body 2701, aprojection system 2702, a mirror 2703, a screen 2704, etc. The presentinvention can be applied to a liquid crystal display device 2808 whichconstitutes a part of the projection system 2702 or other signal drivercircuits.

Note that FIG. 10C is a diagram showing an example of the structure ofprojection systems 2601 and 2702 of FIGS. 10A and 10B. The projectionsystems 2601 and 2702 comprise an optical light source system 2801,mirrors 2802 and 2804 to 2806, a dichroic mirror 2803, a prism 2807, aliquid crystal display device 2808, phase differentiating plate 2809 anda projection optical system 2810. The projection optical system 2810comprises an optical system including a projection lens. The present

Embodiment showed a three plate type, but it is not limited to thisstructure, and it may be for instance a single plate type. Further, theoperator may appropriately dispose an optical system such as an opticallens, a film having light polarizing function, a film for adjustingphase difference and an IR film, in the optical path shown by an arrowin the FIG. 10C.

FIG. 10D is a diagram showing an example of the structure of the opticallight source system 2801 of FIG. 10C. In the present Embodiment theoptical light source system 2801 comprises a reflector 2811, a lightsource 2812, lens arrays 2813 and 2814, light polarizing conversionelement 2815 and a condenser lens 2816. Note that the optical lightsource system shown in FIG. 10D is merely an example and is notspecifically limited. For example, the operator may appropriatelydispose an optical system such as an optical lens, a film having lightpolarizing function, a film for adjusting phase difference and an IRfilm, etc., in the optical light source system.

Provided however, the projectors shown in FIG. 10 show a case of usingtransmission type electro-optical device and an application example ofreflection type electro-optical device is not shown in the figures.

FIG. 11A is a portable telephone, and it includes a main body 2901, anaudio output portion 2902, an audio input portion 2903, a displayportion 2904, operation switches 2905, and an antenna 2906, etc. Thepresent invention can be applied to the audio output portion 2902, theaudio input portion 2903, the display portion 2904 or other signaldriver circuits.

FIG. 11B is a portable book (electronic book), and it includes a mainbody 3001, display portions 3002 and 3003, a recording medium 3004,operation switches 3005, and an antenna 3006, etc. The present inventioncan be applied to the display portions 3002 and 3003 or other signaldriver circuits.

FIG. 11C is a display, and it includes a main body 3101, a support stand3102, and a display portion 3103, etc. The present invention can beapplied to the display portion 3103. The display of the presentinvention is advantageous for a large size screen in particular, and isadvantageous for a display equal to or greater than 10 inches(especially equal to or greater than 30 inches) in the opposite angle.

The applicable range of the present invention is thus extremely wide,and it is possible to apply the present invention to electronicappliance in all fields. Further, the electronic appliance of embodiment6 can be realized by using a constitution of any combination ofembodiments 1 to 5.

According to the present invention, a liquid crystal display devicewhich includes a pixel TFT portion having an n-channel TFT of inversestagger type, and a retention capacitor, can be realized using threephoto-masks by three photolithographic steps.

Besides, in case of forming a protective film, a liquid crystal displaydevice which includes a pixel TFT portion having an n-channel TFT ofinverse stagger type protected by the inorganic insulating film, and aretention capacitor, can be realized using four photo-masks by fourphotolithographic steps.

1. A display device comprising: a pixel electrode over a substrate; aliquid crystal element over the pixel electrode; and a thin filmtransistor, the thin film transistor comprising: a gate electrode overthe substrate; an insulating film over the gate electrode; asemiconductor film over the insulating film; a first electrode over thesemiconductor film; and a second electrode over the semiconductor film,wherein the pixel electrode comprises a transparent conductive materialand is electrically connected to the first electrode, wherein a lean ofa side surface of the gate electrode has a first angle from normaldirection to a top surface of the insulating film, wherein a lean of aside surface of the first electrode has a second angle from normaldirection to a top surface of the semiconductor film, and wherein thefirst angle is larger than the second angle.
 2. The display deviceaccording to claim 1, wherein the pixel electrode is provided over thefirst electrode.
 3. The display device according to claim 1, wherein anend surface of the first electrode is covered with the pixel electrode.4. The display device according to claim 1, wherein an end surface ofthe first electrode is provided substantially in register with an endsurface of the semiconductor film.
 5. The display device according toclaim 1, wherein an end surface of the first electrode is providedsubstantially in register with an end surface of the pixel electrode. 6.The display device according to claim 1, wherein an end surface of thesecond electrode is covered with a transparent conductive filmcomprising the same material as the pixel electrode.
 7. The displaydevice according to claim 1, wherein an end surface of the secondelectrode is provided substantially in register with an end surface ofthe semiconductor film.
 8. The display device according to claim 1,wherein an end surface of the second electrode is provided substantiallyin register with an end surface of a transparent conductive filmcomprising the same material as the pixel electrode.
 9. The displaydevice according to claim 1, wherein the pixel electrode is providedover a capacitor wiring with the insulating film interposedtherebetween.
 10. The display device according to claim 1, furthercomprising a common electrode provided with an opposed substrate. 11.The display device according to claim 10, wherein the liquid crystalelement is provided between the pixel electrode and the commonelectrode.
 12. The display device according to claim 1, wherein the gateelectrode is overlapped with the pixel electrode.
 13. The display deviceaccording to claim 1, wherein the gate electrode is overlapped with acommon electrode.
 14. An electric device comprising the display deviceaccording to claim 1 and at least one of a display module, a battery, animage input portion, an audio input portion, an operating switch and arecording medium.
 15. A display device comprising: a pixel electrodeover a substrate; a liquid crystal element over the pixel electrode; anda thin film transistor, the thin film transistor comprising: a gateelectrode over the substrate; an insulating film over the gateelectrode; a semiconductor film over the insulating film; a firstelectrode over the semiconductor film; and a second electrode over thesemiconductor film, wherein the pixel electrode comprises a transparentconductive material and is electrically connected to the firstelectrode, wherein a lean of a side surface of the gate electrode has afirst angle from normal direction to a top surface of the insulatingfilm, wherein a lean of a side surface of the first electrode has asecond angle from normal direction to a top surface of the semiconductorfilm, wherein the first angle is larger than the second angle, whereinthe pixel electrode consists of a first region and a second region,wherein the pixel electrode is in contact with the first electrode inthe first region, wherein the pixel electrode does not overlap with thefirst electrode in the second region, and wherein an interlayerinsulator is not provided between the pixel electrode and the firstelectrode in the first region.
 16. The display device according to claim15, wherein the pixel electrode is provided over the first electrode.17. The display device according to claim 15, wherein an end surface ofthe first electrode is covered with the pixel electrode.
 18. The displaydevice according to claim 15, wherein an end surface of the firstelectrode is provided substantially in register with an end surface ofthe semiconductor film.
 19. The display device according to claim 15,wherein an end surface of the first electrode is provided substantiallyin register with an end surface of the pixel electrode.
 20. The displaydevice according to claim 15, wherein an end surface of the secondelectrode is covered with a transparent conductive film comprising thesame material as the pixel electrode.
 21. The display device accordingto claim 15, wherein an end surface of the second electrode is providedsubstantially in register with an end surface of the semiconductor film.22. The display device according to claim 15, wherein an end surface ofthe second electrode is provided substantially in register with an endsurface of a transparent conductive film comprising the same material asthe pixel electrode.
 23. The display device according to claim 15,wherein the pixel electrode is provided over a capacitor wiring with theinsulating film interposed therebetween.
 24. The display deviceaccording to claim 15, further comprising a common electrode providedwith an opposed substrate.
 25. The display device according to claim 24,wherein the liquid crystal element is provided between the pixelelectrode and the common electrode.
 26. The display device according toclaim 15, wherein the gate electrode is overlapped with the pixelelectrode.
 27. The display device according to claim 15, wherein thegate electrode is overlapped with a common electrode.
 28. An electricdevice comprising the display device according to claim 15 and at leastone of a display module, a battery, an image input portion, an audioinput portion, an operating switch and a recording medium.